Storage tube system



NOV. l, M, ARDn-l STORAGE TUBE SYSTEM Filed May 26, 1949 4 DELA Y NETWORK im; n P A f- -n m d.: r L@ i. 7A ma LM. A

.s/GNAL SWEEF ATTORNEY Patented Nov. 11, `1952 src STORAGE TUBE SYSTEM Application May 26, 1949, Serial No. 95,397

9 Claims.

This invention relates to storage tube systems and is particularly directed to circuits for tubes of the cathode ray type which may receive signals and electrically store or preserve such signals so that the information thereof may be displayed or utilized at a later time.

The object of this invention is a storage tube system capa-ble of storing for indenite .periods of time the intelligence of signals of short duration.

Another object of this invention is a storage tube system which will receive signals of various amplitudes and faithfully reproduce those signals by appropriate half tones or fractional-tones on a fluorescent screen.

The storage tube of this invention comprises an evacuated envelope containing a screen, a collector electrode disposed adjacent the bomn barded surface of said screen, and a plurality of electron guns. Circuits are connected to beam deflecting means of two guns for systematically and synchronously deflecting the beams of said guns over said surface, one beam lagging or being displaced with respect to the other. Signals are applied to the control grids of said guns, and A means are provided for displacing in time phase the signal on one grid with respect to the other control grid.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing, wherein Fig. 1 shows diagrammatically the storage tube and circuits of this invention, and

Fig. 2 is a functional graph of important target currents and voltages of the storage tube when operated according to this invention.

The cathode ray tube of this invention comprises a storage mosaic or screen l of insulating material, and twoelectron guns 2 and 3 each with the usual accelerating, focusing, and defiecting electrodes for scanning one side of the screen. The cathodes il and 5 of the guns have separate leadein conductors. Across and adja cent the front side of the screen is disposed the collecting electrode 6 for removing secondary and 10W speed primary electrons from the space immediately in front of the screen.

The circuits and structure of Fig. 1 may be better understood by rst referring to some of the electron emission characteristics of low-leakage insulating materials which comprise the bombarded surface of the screen of the cathode ray tube of this invention. These characteristics prevail whether or not the bombarded surface is coated with materials that Will visibly 'liuoresce A screen is presumed, such as glass, the incremental areas of which are Well insulated from each other and from ground so that the potential of each area may float or be individually varied over a wide range of values by the beam. The collecting electrode in front of the screen is maintained at a positive potential with respect to the cathodes and removes any secondary electrons which may leave th-e surface `of the screen with sufficient velocity to clear the space charges at the screen surface.

II the current iiovving to or from the screen is plotted against the screen-cathode potential difference, with a given collector voltage, the characteristics of Fig. 2 result. The collector potential is indicated at Vc, and two different cathode potentials VVW and VE. Since the screen is floating and can be given no charge except by way or" beam current, the static potential of the screen will gravitate or drift during electron inactivity, toward the value of the equipotential line which is adjacent to the screen, usually a potential close to the collector potential. If now electrons are released by the cathode or potential VW and are accelerated in the cathode collector field and reach the screen but with insufficient velocity to dislodge more secondary than arriving primary electrons, the net current to the screen is negative and the rate of drift toward cathode potential is increased. An equilibrium condition is reached when the screen potential becomes equal to the cathode potential at which time the beam is turned back toward the cathode and does not strike the screen any more. As the collector potential increases, the secondary to primary electron ratio increases until, at screen voltage Vo the ratio is one and the net screen current is zero. Once the secondary to primary ratio exceeds one the potential of the target tends to run away toward a value Vn which is approximately that of the collector and may actually be more positive by one or two volts. Hence the target, or any incremental area thereof bombarded by the beam, has two distinct stable potentials, one at the cathode level and the other at the collector level, and the target will assume either potential depending only on Whether the beam energy can carry the target to a potential above Vo. If amplitude modulated signals are applied to the control grid of the electron gun to modulate the beam current, the different bombarded areas of the screen dur- 3 ing scanning may be charged to voltages V1, V2, V3 Vn, the voltage parameters being adjusted so that maximum signal amplitude will carry the eifected screen area to the maximum screen .voltage near the collector Voltage Vn. For practical purposes Vn equals Vc with negligible error.

The display by fractional tones on a fluorescent screen of signal amplitudes corresponding to target voltages V1, V2, Vs Vn will now be described. Signals to be stored are applied directly to the grid of gun 2. Biasing source 'l and leakage resistor 8 are included in the input circuit of this gun. The high direct voltage source 9 is connected to the accelerating anode, and through the load resistor lll to the collector electrode 6. The cathode of the second gun is connected to an intermediate point of the high voltage source, and hence is maintained at a potential, VE, above the other cathode. Signal currents flowing in the collector circuit producevoltages across the load resistor I9 which are applied to the input of a conventional cathode ray display tube ll with gun I2 and fluorescent screen I3. These signal voltages are also applied t0 the control grid of the second gun 3 after amplification at Hl. The amplified signals, also, are shifted in time phase by the time delay network I5. Horizontal and vertical deflections of the beams may be by conventional electrostatic denection plates or magnetic deflection coils. For simplicity of disclosure, one pair of deflection plates are shown for each electron gun as I3 and il with conductors to two sweep voltage sources I8 and i9, the operation contemplated requiring a slight phase difference in the two sweep voltage to cause one beam to lag a distance d behind the other. The display tube beam moves in step with the beam of gun 2. For scanning inthe second dimension, a second pair of deflection plates would be connected in the usual manner to appropriate sweep voltages, the sources of which are not shown.

In operation, the potential Vw of the writing beam cathode ll is such that Vc-Vw Vo, Vc being the potential of the collector electrode 6. If amplitude modulated signals are now applied to the grid of the writing beam gun 2 respective target areas on the screen l are charged to potentials V1, V2, V3 Vn corresponding to the intensities of the writing beam current I1, I2, I3 In, with V1 V2 V3 Vn if I1 I2 I3 11 as shown in Fig. 2. Normally for any given beam current intensity the equilibrium of the potential of the target is Vn, but if the charge disposed by the writing beam in one scan is not of sufficient magnitude the target will be brought only to some lesser potential. Further bombarding of the target will tend to raise the lesser potential toward Vn. If the writing beam is turned off and gun 3 is utilized as an erasing beam whose cathode potential VE is such that Vn-VE V0, the erasing beam will bring back the Whole target area to a potential VE. The duration of the erasure lwill depend upon the intensity of the "erasing beam current. If this intensity is high it will bring the target quickly down to a potential VE. If the erasing beam current is zero it will of course not change the potential V1, V2, 'V3 Vn. The operation of the invention is based on this principle. It follows then that when amplitude modulated signals are applied to the control grid, the writing beam will charge certain screen areas during scanning to voltages V1, V2, V3 Vn related to the amplitude of th lmodulated beam current.

The signals on the grid of gun 2 are then discontinued as by switch 20, and the beam of gun 2 is used as a sampling beam with a constant beam current amplitude and the same cathode potential Vw with respect to the collector potential Vc. As the sampling beam scans the target, the current collected by the collector electrode will depend on the potential V1, V2, V3 Vn on the screen, and a variable signal voltage will appear across the resistance I0 in the collector circuit which Will reproduce the stored amplitude-modulated signals. But, because of the scanning by the sampling beam, each potential V1, V2, Vs will be displaced a certain amount toward Vn. It is the function now of the erasing beam to restore these displaced voltages to their original values V1, V2, V3 V11, to which end, the signal voltage across resistance Il] is fed back to the grid of gun 3 of the erasing beam. In addition to amplification at I4, the feed back voltages are shifted in time phase by the delay line or network I5, the amount of phase shift being adjusted to equal the phase displacement between the two beams. The time of delay of line I5Y can of course be easily calculated from the distance d between the beams and the velocity of scanning. I-Ience, the intensity of the erasing beam current will be modulated in amplitude and in the proper phase to change the potentials of the various target areas back to V1, V2, V3 Vn, and when the sampling beam makes the second scanning, the potentials encountered on the target will be the same as the original potentials. By the sampling beam scanning in the front of the erasing beam the original information may be stored indefinitely.

For display of the stored information, the signal voltages developed across collector resistance le may be applied to the grid of a cathode ray tube Il, the sweep voltages of which are synchronized with the sweep voltages for the sampling beam. The entire useable range of signal levels received and stored may be brought within the range of visible fluorescence of the display tube screen so that the signal can be accurately displayed with realistic half-tones or fractionaltones. The signal voltages across collector resistance I0 may of course be applied to other utilization circuits and devices, such as computors or switch controls, etc.

To erase the picture stored on the screen, it is only necessary to interrupt the sampling beam, as by a cut-off grid bias, and let the erasing beam continue to scan the screen for a few frames until the entire target area is brought to the potential VE of the erasing beam cathode 5. The system is then ready for another storage cycle. The storage system of this invention is thus capable of storing for indefinite periods of time the intelligence of signals of short duration and will faithfully reproduce or display those signals by appropriate fractional-tones on a fluorescent screen.

While the above described principles of this invention are in connection with specific apparatus, it is clearly understood that this description is made only by way of example and not as a limitation to the scope of this invention.

What I claim is:

1. A cathode ray tube storage system having a storage mosaic for storing variable electrical information, means for scanning said mosaic for deriving said stored information, a second scanning means for applying electrical charges to said mosaic, and a feedback circuit for 'applying a control signal in response to said derived information to said second scanning means for restoring the electrical information on said mosaic removed by said first mentioned scanning means.

2. In a storage device for variable electrical information comprising a storage mosaic, means for scanning said mosaic for storing said variableelectrical information, means for scanning 'said mosaic for deriving said stored information, andv means under control of a portion of said derived stored information for scanning said mosaic to.

restore substantially the charge removed from said mosaic by said second mentioned scanning means.

3. An arrangement according to claim 2, fui'- ther comprising means for synchronizing the scanning of said second and third mentioned scanning means, means for phase displacing the scanning of said second and third mentioned scanning means a given amount, and means for delaying said portion of said derived stored information said given amount before utilizing it to control the scanning of said third mentioned scanning means.

4. An arrangement according to claim 1, wherein each of said scanning means comprise an electron beam source associated with said mosaic, and means for modulating the intensity of said first scanning means in accordance with said variable information for storing said information, and means for varying the intensity of said second beam under control of said derived information to restore the charge removed b said rst mentioned scanning means.

5. An arrangement according to claim 4, comprising a load circuit and means for applying another portion of said derived stored information to said load circuit.

6. An arrangement according to claim 51 wherein said load circuit comprises a cathode ray tube and means for applying said another portion of derived information to said cathode ray tube for displaying said stored information.

7. An arrangement according to claim 6, comprising means for scanning the cathode ray beam of said oscilloscope in synchronism with said other scanning means.

8. An arrangement according to claim 1, wherein said scanning means for deriving said information comprises a xed intensity cathode ray beam.

9. An arrangement according to claim 8, comprising means for intensity modulating the beam source of said rst scanning means with said variable information for storing said variable information on said mosaic, the beam source of said second scanning means having a xed intensity, means for scanning said last named beam source over said mosaic for deriving said stored information, said third mentioned scanning means comprising means for modulating said second beam with a portion of said derived information for restoring the charge removed by said fixed intensity beam source.

MAURICE ARDITI.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 2,130,134 Iams Sept. 13, 1938 2,147,760 Vance et al. Feb. 21, 1939 2,219,021 Riesz Oct. 22, 1940 2,245,364 Riesz et al. June 10, 1941 2,301,743 Nagy et al. Nov. 10, 1942 2,324,534 Pierce July 20, 1943 2,369,749 Nagy et al. Feb. 20, 1945 2,430,038 Wertz Nov. 4, 1947 2,437,173 Rutherford Mar. 2, 1948 2,449,536 Wolff Sept. 14, 1948 2,454,410 Snyder, Jr. Nov. 23, 1948v 2,468,100 Moskowitz Apr. 26, 1949 2,481,458 Wertz Sept. 6, 1949 

